Tires are an essential component on virtually all motorized and towed (freewheeling) vehicles. They are typically mounted on rims, and most are filled with pressurized air (or another gas) to maintain the tire's round shape under load. The pressure provides needed shock absorption upon contact with obstructions and allows the tire's contact surface to comply during turns for enhanced maneuverability. Tires are generally constructed from a durable elastomeric compound that applies significant friction to a confronting ground surface. This tire compound can include natural and/or synthetic rubber in a number of formulations that pored into a tire mold as a formable solid, and subsequently hardened and cured into the finished tire. The inner structure of the tire (between the inner and outer surface) is reinforced with plies of synthetic fiber, such as nylon that are laid in place at the outset of the molding process.
In the case of road tires, the radial design currently predominates. In radial tires the piles are oriented radially, being generally perpendicular to the bead (the portion which engages the rim and seals in pressurized air). The internal structure of the tread or contact face may also include steel belts for added durability. Bias-ply tires are often used in industrial and agricultural applications (e.g. loaders, construction vehicles, farm equipment, tractors, and the like), in which the alternating layers of plies cross each other, and each oriented at a non-perpendicular angle relative to the bead. The bias-ply design typically allows the tire to support greater loads for a given size, rendering it desirable for slower-moving and off-road industrial vehicles. Nevertheless, radial tire designs are becoming more-popular in certain industrial applications.
Tires designed for road-traveling vehicles, such as cars, trucks and trailers are designed with higher-speed performance and handling as a primary design parameter. Treads tend to be shallow and the surface area contacting the road tends to be a large proportion of the overall surface. Thus, the grooves surrounding the treads are fairly narrow and shallow. This type of tread design serves several purposes. It ensures that the contact surface is sufficiently large to provide sufficient frictional grip at high speeds and in sharp turns. This large contact surface also reduces tire wear and increases tire life at high speeds—the larger the contact surface area, the smaller the localized friction, and hence, the lower the wear. Because road-going tires generally encounter fairly smooth surfaces, without significant obstructions, the shallow tread is generally no detriment. Sometimes mud and snow impede their performance, but overall, this tread design is a reasonable tradeoff between high-speed performance and traction in adverse road conditions.
However, tires for use on industrial vehicles may spend virtually all of their operative time off-road, and often on very rough, wet and/or muddy surfaces. Typically, high-speed handling and performance are not concerns. Rather, tread designs for industrial tires mainly focus upon the width and size of grooves between tread lugs. The lugs are high, and often narrow, so as to provide an aggressive contact surface that maintains maximum traction, even in the wettest and most loosely-compacted terrain. In many cases, failure to maintain positive traction renders the vehicle useless in its task—for example, a bucket loader that must stand firm while driving the bucket into a mound. Of course, this tread design would lead to significantly higher wear rates and lower stability at high speeds due to the reduced road-contact area of the lugs. In most instances the aggressive tread profile is not detrimental to the vehicle's function, as such vehicles rarely take to the highway, and/or when they do, it is at very low speeds and/or for short distances.
The changing economics of farming create a significant exception to this general tread-design rule. In the U.S., and worldwide, many small-to-midsize farm properties are being consolidated under a single owner operator of farm equipment. Often these properties are non-contiguous and somewhat geographically remote from each other, being separated by hundreds of yards, or even hundreds of miles. The small size of individual farm parcels makes the use of separate equipment for each parcel uneconomical. Rather, the farmer is motivated to transport his or her equipment between non-contiguous parcels as needed. Such transport occurs over public roads that adjoin and connect the parcels.
Some equipment is simply carried on roadworthy trailers and trucks. Other equipment, owing to its size and weight, must be transported in direct contact with the road. FIGS. 1 and 2 detail one such equipment type. In this example, a manure-spreading trailer 100 (sometimes termed in the industry as a “honey wagon”), towed by a conventional, heavy-duty tractor 210, is shown transitioning from the farm field 212, where it has deposited liquid manure to a county road 214 that adjoins the field. The tractor 210 and hitched trailer 100 are being transported to a non-contiguous field or other location via the county road 214. The trailer 100 in this example is a conventional Model EL48-8D spreader available from J. Houle & Fils Inc. of Drummondville, Quebec, Canada. This trailer includes a liquid manure tank 110. It supports its heavy load on eight large independently steered wheels 120, each carrying a tubeless, pneumatic tire 130. The exemplary tire is a size 28L×26 ANS model, with an R-3 type lug tread, available form Bridgestone-Firestone of Nashville, Tenn. This tire is characterized by a relatively curved contact surface and a fairly conventional cloverleaf-style tread pattern in which a tessellated geometry of diamond-like lugs are separated by adjoining grooves.
The prior art tire has a tendency to accumulate a large volume of accreted mud, biomass and other soft detritus 140. This is because the profile of the contact surface 150 is curved, and the grooves 152 (see inset FIG. 1A) between tread lugs 154 are isolated from each other, giving mud, etc., no path to escape. As shown in detail in FIG. 2, this accumulation tends to follow the tire as it transitions onto the solid road surface 214, where it is then ejected in tracks 230 that clutter the road. As a matter of good citizenship, and often as a matter of law, the operator 240 must stop to clean all the ejected detritus from the road 214, expending time, energy and placing the operator at risk to be struck by a passing vehicle (250). In addition, once the road 214 is cleaned, the trailer 100 will make its trip on tires that are not well-suited to a hard road surface, as they are particularly adapted to field use. Given the high degree of contact surface curvature, and aggressive tread, the prior art tires wear quickly, particularly when driven on hard road surfaces at speed. In addition, their handling is unsuited to higher speed driving. In cases where the trailer is to be driven long distances, it may be connected to a conventional truck and driven at such higher speeds-up to, and including, highway speeds.
Notably, where the farm vehicle is a freewheeling, towed unit, the tires need not exhibit an extraordinary degree of traction. Rather, their primary function is to support the vehicle and maintain it in a straight line as it is towed around the field. Many other forms of self-propelled agricultural equipment, including combines, threshers and harvesters can also operate effectively with tires having a less aggressive tread due to their weight and overall footprint. Accordingly, it is highly desirable to provide an improved tire for use in such vehicles that reduces the accretion of mud and other detritus, provides improved handling on hard roads and exhibits increased wear resistance.